Methods of and means for reducing noises and vibrations produced by screw propellers of ships



July 31, 1956 2,756,713

i... KORT METHODS OF AND MEANS FOR REDUCING NOISES AND VIBRATIONSPRODUCED BY SCREW PROPELLERS OF SHIPS Filed Dec. 10. 1952 /IIIIIII41,111,.

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M'TURNE Y United States Patent METHODS OF AND MEANS FOR REDUCING NOISESAND VIBRATIONS PRODUCED BY SCREW PROPELLERS OF SHIPS Ludwig Kort,Hannover, Germany Application December 10, 1952, Serial No. 325,198 '6Claims. (Cl. 1'1542) This invention relates to methods of and means forreducing noises and vibrations produced by screw propellers of ships.

On screw-propelled ships the turning of the propeller or propellersalmost always produces pronounced v1- brations and noises, the sourcesof which vary somewhat on single and on twin screw ships and also dependupon the position of the propeller with respect to the ships hull.

One of the objects of the present invention is to provide methods of,and means for, avoiding or at least reducing the vibrations and noisesby reducing the sources of the impulses causing the vibrations or noisesand by preventing the increase of the vibrations and noises byresonance.

The blades of a propeller turning near the stern of a ship meet on theircircular path with water moving at difierent speeds caused by the wakedistribution. Since the pitch of the propeller blades is uniform for atleast each radius, they receive a shock each time a blade is passingthrough a zone of greater wake. One way to reduce such shocks somewhatis to reduce the pitch of the blade tips because in that case they acton a lever of about the total length of the blades. However, by thisarrangement it is impossible to avoid reducing the propulsiveefiiciency. By the choice of an intermediate pitch of the blade tipscorresponding to a mean acceleration of the water between the fast andthe slow access speed of the water, the shocks and, therefore, theimpulses producing the noises and also the said loss of propulsivethrust will be reduced to the practical minimum.

When the propeller is shrouded by a double-walled ring known in the artas a Kort nozzle and disclosed in Patents Nos. 2,030,375 and 2,566,525,the water is pre-accelerated between the mouth of the nozzle and theturning circle of the propeller and this of its own helps to minimizethe shocks. On nozzle-enclosed propellers, it is also customary toreduce the pitch at the blade tips; however, in this case, chieflybecause in their zone the speed of the water is reduced by its frictionat the walls of the mouth part of the nozzle. In addition, there is afurther possibility of equalizing the speed of the water arriving at thepropeller disc by lengthening the nozzle body in front of the propellerwithin the zone of greatest wake. By this means, the fastest movingwater, i. e. in the annular zone halfway between the tips of thepropeller and the axis of the propeller, has time and additionaldistance to increase the speed of the slow moving water by frictionbefore it reaches the propeller.

The present invention provides a method of reducing vibrations and noiseproduced by a screw propeller of a ship, consisting in considerablythickening the ships structural materials adjacent to thenoise-producing parts and (or) in fitting anti-vibration andnoise-absorbing material onto the plating or filling the entire spacebetween two opposed plates solid with the anti-vibration andnoise-absorbing material. The propeller blade tips are given a pitchwhich preferably corresponds to an intermediate acceleration of thewater between the fastest and the slowest moving water at the bladetips.

In the case of a ship in which the propeller is shrouded by a nozzle,the method may consist in using heavy plating adjacent to the passingpropeller blades and (or) fitting anti-vibration and noise-absorbingmaterial to or between the plating of the radial sections of the nozzlebody in the zone near to the propeller circle, or over the whole lengthof the radial sections.

constructional forms of the invention are shown by way of example on theenclosed drawing, on which:

Fig. 1 shows the stern end of a twin screw ship in which, in the regionof the propellers, the plating itself is either thickened or coveredwith a thick layer of noise-absorbing material;

Fig. 2 shows a Kort nozzle which, in the upper radial section, ispartially filled with anti-vibration and noiseabsorbing material, andwhich in the lower radial section is entirely filled with such material;

Fig. 3 also shows a Kort nozzle, the plating of which is covered on itsinner surface with a layer of anti-vibration and noise-absorbingmaterial; and

Fig. 4 is a side view of a Kort nozzle designed to meet the desiredrequirements referred to above. The length of the nozzle in front of thepropeller disc is greater near to the underside of the stern of the shipthan in the other portions because near to the ship there is the zone ofgreatest wake.

Referring to the drawings:

When the blade tips of a propeller (e. g. on a twin screw ship) pass theshell plating of the hull, alterating pressure and suction forces areproduced by which the plating tends to buckle and to move back as soonas the blade tips pass near to it and recede from it.

These movements of the plating are repeated each time the propellerblades come near to the hull and thereby produce strong vibrations andnoises which are increased by the resonance of the adjoining shellplating.

When the distance between the blade tips and the hull plating is smallor when the blades pass the pro peller post or other appendages settingup no vbirations of their own, nevertheless there will always be achange in the speed and the direction of the water leaving the bladetips. Furthermore, there may be formation of cavitation at these places,both producing a considerable noise which can be observed even at placesfar removed.

These disadvantages are reduced or are entirely avoided either bythickening the shell plating, the propeller boss, the struts for thepropeller bearings considerably or by fastening on the inside of theplating a layer a (Fig. 1) of material having qualities by which thevibrations are reduced, and such material may, for example, consist ofconcrete, light Weight concrete, rubber, wood, marineglue, artificialresin or similar products.

On propellers which are shrouded by a nozzle, the distance between theblade tips and the inside plating of the nozzle is uniform all around.Nevertheless, a humming noise will be observed due to local vibrationsof the nozzle plating when the blade tips are passing it. This noise canbe greatly reduced by using heavy plates adjacent to the passingpropeller tips or by filling the space between the inside and theoutside of the nozzle body with the above mentioned anti-vibration andnoiseabsorbing material.

On the upper of the two radial sections through the nozzle, Fig. 2 showsa part-filling with such anti-vibration and noise-absorbing materialwhile the opposite radial section illustrates the manner in which thewhole nozzle ring may be filled out with such material. In some cases,it may not be necessary to fill up the space between the inside and theoutside plates for it may be sufficient to cover or to line the insideof the plating with a layer of anti-vibration and noise-absorbingmaterial as indicated by Fig. 3.

Having thus described my invention, I claim:

1. Apparatus for reducing the vibrations and noise pro'duce'd'by therotation of a screw propeller of a vessel, comprising, adoubl'e wallednozzle ring surrounding the periphery of the propeller circle, and antivibration material filling the inner hollow space between the walls ofthe nozzle ring.

2. The apparatus of claim 1 wherein the anti-vibration material isconcrete.

3. The apparatus of claim 1 wherein the anti-vibration material islimited to the area between the walls adjacent the periphery of thepropeller circle.

4. Apparatus for reducing the vibrations and noise produced by a screwpropeller, including propeller blades, the pitch of which adjacent thetips corresponds to an intermediate acceleration of the water betweenthe fastest and slowest moving Water arriving at the blade tips, nozzlemeans forequalizing the speed of water arriving at the propeller discand vibration damping means-included in 'thenozzle adjacent theperiphery of the propeller tips.

5. Apparatus for reducing the vibrations and noise produced by therotation of a screw propeller of a vessel comprising, a double walledKort nozzle ring surrounding the periphery of the propeller turningcircle and a layer of noise-absorbing material fitted to the inside ofthe double walls of the nozzle body in the zone of the turning circle ofthe blade tips of the propeller.

6. Apparatus for reducing the vibrations and noise produced by therotation of a screw propeller of a vessel comprising a double walledKort nozzle ring surrounding the periphery of the propeller circle and alayer of noiseabsorbing material fitted to the inside walls of thenozzle body covering the whole inside of the walls around the innerhollow space of the nozzle ring.

References Cited in the file of tl is patent UNITED STATES PATENTS 856,1I5 Wadagaki June 4, 1907 1,801,875 Nelcher Apr. 21, 1931 1,987,708Rcplogle Jan. 1.5, 1935 2,030,375 Kort Feb. 11, 1936 2,127,475Yourkevitch Aug. 16, 1938 FOREIGN PATENTS 143,286 Great Britain May 7,1920 217,918 Germany Jan. 17, 1910 332,188 Great Britain July 14, 1930853,715 Germany Oct, 27, 1952

